# def city_country(city, country):
#     return f"{city.title()}, {country.title()}"

# def city_country(city, country, population):
#     return f"{city.title()}, {country.title()}, Population {population}"


def city_country(city, country, population=None):
    if population:
        return f"{city.title()}, {country.title()}, Population {population}"
    return f"{city.title()}, {country.title()}"